Flexible shafts comprise basic elements of power transmission and are designed to transmit rotary motion or control from a driving element to an element to be driven. Transmission may be over, under, or around obstacles or objects where transmission by solid shafts would be impractical or impossible.
In a typical rotatable flexible shaft, a central wire mandrel has a plurality of layers of closely coiled wire wound thereover, each of the layers being successively wound over another in alternately opposing directions, i.e., right or left-hand lay. This shaft may be covered by a flexible casing and a clearance between the shaft and casing is provided in order that the shaft may rotate freely within the casing.
Another type of rotatable flexible shaft does not include a wire mandrel but is provided with a central hollow bore for receiving a soft solid metal wire therewithin. The shaft and wire may then be curved to a desired configuration for routing around or between components. Such a hollow shaft is fabricated by winding the strands over a solid mandrel, heat treating the strands, and removing the mandrel.
The present rotatable flexible shaft may be used in power driven or remote control applications and employs such a hollow flexible shaft as an outer torque carrying member as well as an electrical current carrying member. An electrically insulating flexible tube is received within the hollow bore. Disposed within the hollow bore is an inner rotatable flexible shaft, capable of transmitting torque while rotating. The inner shaft may be impressed with an electrical polarity opposite to the outer hollow shaft, thus enabling a circuit to be completed through the shafts. The inner shaft may function as a push-pull element, as well as a rotatable element, while current is passing therethrough, and while the outer shaft is rotating. An outer protective casing may be provided.
A principal advantage derived from the practice of the present invention resides in a savings of space and weight, as well as components which would be needed if separate flexible shafts and electrical connections were required between driving and driven members.